Membrane-liner and process of manufacture



May 24, 1966 J. R. BENSON 3,252,851

MEMBRANE-LINER AND PROCESS OF MANUFACTURE Filed Feb. 1B, 1965 2Sheets-Sheet l 1N VEN TOR.

Jewell R. Benson F'g 5 BY wHlTEHEAD, voGL a LowE ATTORNEYS May 24, 1966J. R. BENSON MEMBRANELINER AND PRocEss oF MANUFACTURE Filed Feb. 18,196:5

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United States Patent O 3,252,85ll MEMBRANE-LINER AND PRUCESS OFMANUFACTURE Jewell R. Benson, 1035 th St., Denver 2, Colo. Filed Feb.18, 1963, Ser. No. 260,343 8 Claims. (Cl. 161-236) This inventionrelates to membranes and linings and more particularly to impermeablemembranes and linings for general construction purposes, a primaryobject of the invention being to provide a novel and improvedimpermeable sheet material which may be used as a water and vaporbarrier membrane in certain types of constructions and also as a waterretaining liner in other types of constructions. As such, the inventionwill be hereinafter referred to as a membrane-liner.

This application is a continuation-impart of rny -application for amembrane-liner, led June 23, 1961, Serial No. 119,098, now abandoned, toinclude the results of tests, di-scoveries and developments subsequentto that time which are herein disclosed to better enable the public tounderstand, know the limitations of, and to practice the invention.Subsequent to the filing of the application, it was discovered that thecritical temperatures could be higher than those originally disclosed,that prompt cooling was an extremely importantfactor to the long life ofthe product, that only certain classes of vinyl chloride sheets could beused to produce a product with the components being adequately bondedtogether and having the toughness and ductility needed for severe fieldusage.

A variety of membranes and liners are commonly `available and asphaltand asphalt impregnated sheets are often used for this purpose becauseof the impermeability of asphalt, the ease with which they may be formedand the low cost. A very simple liner may consist of a sheet of asphaltsaturated felt, however, the application of such a liner material islimited because of its low strength and brittleness, especially 'afteraging a few years. More often, felt sheets are mopped or welded togetherwith alternating layers yof asphalt and asphaltic materials to form amembrane or liner of appreciable thickness, increased strength andresistance to aging. In another, better, type of lining a ve-elementcomposition is used, including a central core of asphalt, a mineral llerand a iibrous material such as felt, asbestos and glass libre. The coreis covered with asphalt saturated lfelts which are, in turn, weathercoated with asphalt.

The patent to Bramble, No. 2,771,745, issued Nov. 27, 1956, is exemplaryyof a laminated asphaltic lining material. Such lining is necessarilymade in thicknesses of one-fourth to one-half inch and this impartsa.severe commercial disadvantage because of the weight and shippingcosts involved. This is a heavy material having low tensile strength andwill break easily when not carefully handled when being shipped andinstalled.

Certain types of synthetic resins and especially the polyvinyl chloridepolymers are available yas sheets or Webs and because of theirimpermeability, they are also' used as membranes in some structuralapplications. Also, some types of polyvinyl chloride polymers, whichwill be hereinafter referred to as polyvinyl chloride, are very ductileand are capable of being elongated as much as 200 to 300% of theiroriginal length. This is contrasted with other types which resistelongation and which are almost brittle. Polyvinyl chloride types ofsynthetic resins, hereinafter referred to as polyvinyl chloride are asyet quite expensive and thus comparatively thin sheets of the materialare used for membrane purposes. This disadvantage is offset in many waysby the toughness, ductility and pliability of certain selected types ofthe material and it has been proposed to line ice comparatively largeareas, such Ias a reservoir basin, with a thin membrane of polyvinylchloride. The results of attempts to do so were generally unsatisfactory-because of the dilculty in handling the material and the diculty ofjoining the edges of individual sheets. For example, the slightest Windaction lbillows and tears the sheets as they are placed 4and before theycan be protectively covered. Also, although tough, ductile and pliable,the sheets are easilyv cut or punctured by small sharp objects such ascrushed rock. Moreover, expensive, toxic solvents or special electronicor other heating equipment is required to join and weld edges ofadjacent sheets. Another disadvantage lies in the adverse aging eiectsof the material when exposed to -air and especially to sunlight since itwill become comparatively hard and brittle.

It has been proposed to combine polyvinyl chloride sheets with othermaterials and especially asphalt to obtain an improved product havingthe advantages of both the `asphalt and the synthetic resins. The patenttoI Bove, No. 2,893,907, issued July 7, 1959, is exemplary of alaminated material using layers of polyvinyl chloride and asphalt.However, this lproduct and other products available which endeavor tocombine the materials have been developed for special purposes andlimited applications.

One factor which has inhibited development of improved membranes andliners by combining these materials, other than by using rigid types ofpolyvinyl chloride sheets, such as disclosed by Bove, lies in the factthat a suitable weld-bonded laminate combination of coherent ductilityhas proven to be unattainable. This is because the softening pointtemperatures of the synthetic resins and especially selected typespolyvinyl chloride, which have desirable properties of elongation,toughness, and ductility, is as low as, or lower than the temperaturesnecessary to render asphalts, suitable for the purpose at hand,sufficiently iluid, to be worked. The types of Iasphalts which melt attemperatures below the softening point temperatures of ductile polyvinylchloride sheets are so soft at ordinary temperatures that they `are notsuitable for laminated -asphaltic lining materials. When a soft, lowsoftening-point asphalt is used in such a liner, theliner will not:adequately bond to the synthetic resin sheet, Will sag under stressrand be very difficult to handle in installation, and once installed atan exposed location and on the slightest slope the layers Will slip andthe liner Will come apart the first hot day of summer,

A further problem in the development of a membraneliner using asynthetic resin between layers of asphalt lies in the existence offactors which lead to deterioration lof the resin. Many types ofsynthetic resins are not at all compatible with asphalt and in thisregard vinyl chloride appears to be one of the best practical materials.It adheres to asphalt under appropriate temperature conditions with anexcellent bond without a tendency for the plasticisers or otherconstituents in the polyvinyl chloride to migrate to the surface `of theresin and destroy the bond thereto. Nor do the oils or otherconstituents of the asphalt tend to migrate into the resin to adverselyeffect either the bond or the properties of the resin.

Overheating of the resin, however, is an important and critical factor.Under the influence of heat, the vinyl chloride will break downreleasing chlorine and free carbon. This causes the material to turnblack and also to become very brittle. Small amounts of chlorineproduced in the first few seconds of heating will actually catalyze thebreakdown process causing it to speed up. To counteract this, ordinarycommercial polyvinyl chloride will include stabilizers such as tribasiclead stearate, epoxies and cadmium and barium soaps. These stabilizersare chlorine acceptors which hook onto the first wisps of chlorine andtherefore impede the catalyst action. Such stabilizers cannot completelyinhibit breakdown of the material under sustained influence of heat butthey can delay breakdown for remarkable periods of time.

There is a real and denite need for an improved general purposemembrane-liner which is sufficiently rigid to be handled ascomparatively large flat sheets such as the liner material disclosed byBramble, and which has the advantages of asphalt-impregnated felt sheetsand asphalt layers integrally supplementing the toughness, ductility andpliability possible only with 'selected ductile types of syntheticresins such as polyvinyl chloride. A liner material is also needed whichis not thick and as heavy as the one-fourth inch to one-half inch sheetsof the type disclosed by Bramble, now -in common use.

It was with such factors in View, that the present invention wasconceived and developed and the invention comprises, in essence, amembrane-liner formed as a wellbonded laminate of compatible asphaltlayers and a sheet of a selected ductile type of polyvinyl chloridebetween sheets of saturated felt. The invention includes further, uniqueand simplified steps in a process of manufacturing the membrane-liner tointegrate the polyvinyl chloride with and between layers of selectedasphalt having a working fluid temperature as great or greater than thesoftening or melting temperature of the synthetic resin by takingadvantage of a discovery that a polyvinyl chloride type synthetic resinapparently requires a time lag to lose its strength and to soften whenheated to its softening temperature, and also that heating followed byquick cool* ing, or quenching of the laminate does not adversely affectthe polyvinyl chloride sheet to a degree where breakdown of the materialis serious or critical.

It follows that an object of the invention is to provide Va novel andimproved membrane-liner which advantageously presents a sheet ofpolyvinyl chloride thermally bonded to layers of a selected type ofcompatible asphalt as a core sandwiched between sheets of asphaltsaturated felt to obtain a moderately flexible membrane-liner which issufficiently rigid to be easily handled in shipping and in installation,to combine the toughness and ductility of the polyvinyl chloride withthe compatible properties of its covering layers and with the stiffeningand shape retaining effect of the asphalt saturated felt sheets and toeffectively armor plate the polyvinyl chloride sheet against weatheringeffects with enhanced immunity from puncture or tear by sharp objects.

Another object of the invention is to provide a novel and improvedmembrane-liner which is especially adapted for use in a building orstructure as a moisture and vapor barrier, as in a floor or wallsection, and which is also well adapted to be used as a liner within anearth body surrounding a structure, as to protect the structure from theeffects of moisture, and especially frost action.

Another object of the invent-ion is to provide a novel and improvedmembrane-liner which may be furnished as sheets which are not undulythick and heavy, which are easy to handle, easy to join and which areespecially suitable for lining reservoirs, ponds and like basins andwhich will require a minimum of protective covering material after thelining.

A further object of the invention is to provide a novel I and effectivemethod for the manufacture of an improved membrane-liner having a sheetof polyvinyl chloride thermally bonded to and between layers of aselected compatible asphaltic material in a rapid efficient manner andin a manner which accommodates the use of ductile asphalts havingcomparatively high softening point temperatures, and workable uidtemperatures.

. A further object of the invention is to provide a novel and effectivemethod for the manufacture of an improved membrane-liner having a sheetof polyvinyl chloride integrally combined with compatible asphalticmaterials at comparatively high bonding temperatures, with immediatecooling action in a manner which advantageously A. tempers and toughensthe resulting laminate sheet of polyvinyl chloride and asphalt to adesirable degree without permitting significant deterioration andbreakdown of the vinyl chloride resin.

With the foregoing and other objects in view, all of which more fullyhereinafter appear, my invention c0mprises certain improvedconstructions, combinations and arrangements of parts and elements andcertain steps, sequences and operations as hereinafter described,defined in the appended claims and illustrated in preferred embodimentin the accompanying drawing, in which:

FIGURE 1 is a perspective view of a rectangular sheet of amembrane-liner constructed in accordance with the principles of theinvention, and with portions of a corner being broken away to show thelaminated character of the construction.

FIGURE 2 is a fragmentary sectional detail of the membrane-liner asviewed from the indicated line 2 2 at FIG. l but on a greatly enlargedscale to better illustrate the character and co-action of the materialsforming the laminated construction.

FIGURE 3 is a fragmentary edge View of the corner portions of twoadjacent sheets abutted together and interconnected by a joint strip.

FIGURE 4 is a fragmentary edge view of the corner portions of twoadjacent sheets as being joined together with one shee-t overlapping theother.

FIGURE 5 is a diagrammatic perspective view of a roll of themembrane-liner illustrative of an alternate manner of furnishing thematerial, as at an installation where long unbroken lengths of themembrane-liner are desired.

FIG-URE 6 is a diagrammatic fragmentary sectional view of a portion of astruc-ture wherein the improved membrane-liner is embedded, andillustrating further, in a somewhat exaggerated manner, a shrinkagecrack and offsetting movement such as will occur in many types ofstructures and the manner in which the unique core component of themembrane-liner will stretch and otherwise function to prevent rupturethereof and failure of the membrane-liner as a water or vapor barrier.

FIGURE 7 is a diagrammatic fragmentary sectional View of a portion ofthe improved membrane-liner as lying upon and covering a bed havingsharp pointed rocks therein and illustrating further the manner in whichthe unique core component of the membrane-liner will yield to furtherresist puncture, as by an object which will ordinarily puncture amembrane made only of asphalt saturated felt sheets and asphalticmaterials.

FIGURE 8 is a diagrammatic layout, along a longitudinal axis, of apreferred arrangement of apparatus carrying the essential webbingmaterials and bringing these materials together to form a uniquely coredmembrane-liner in accordance with the principles of the invention.

FIGURE 9 is a graphic diagram illustrating the relationship of tensilestrength and ductility of a selected type of a polyvinyl chloride sheetto temperature.

FIGURE 10 is a graphic diagram illustrating the relationship betweenviscosity and the temperature of compatible types of asphalts used inthe practice of the mvention.

FIGURE 11 is a graphic diagram, associated with FIG. 8 illustrating therelationship of temperature to the movement of material through theapparatus and to the point where it cools to solidification.

.FIGURE 12 is a diagrammatic section detail of certain components of theapparatus as taken from the indicated line 12-12 at FIG. 8 but on anenlarged scale.

Referring more particularly to the drawing, the improved membrane liner20 is a laminated sheet having sheets of asphalt saturated feltprotectively overlying al core comprised of la central sheet 21 ofpolyvinyl chloride type synthetic resin heat welded to and betweenlayers of compatible asphalt. The preferred construction of themembrane-liner, as illustrated at FIG. 2, is a symmetrical arrangement,including a core surface layer 22 of asphalt of a type hereinafterdescribed thermally bonded to each side of the central sheet 21, areinforcing sheet 23 of a sa-turated felt added to the outer side ofeach core layer 22 anda protective layer 24 of asphalt, of a typehereinafter described, 'at the outer side of each reinforcing sheet 23.In addition, other coatings, not shown, may cover the protective outerlayers 24, one such cover material commonly used being With such coreand layers the membrane-liner may be manufactured to vary in thicknessfrom 1/16- inch to rvVle-inch and the thickness and character of thematerials must be such that the sheets are comparatively rigid and easyt-o handle. It has been found that -a sheet 1/s-inch -thick ispreferable for many commercial purposes.

For practical handling of the membrane-liner, it has been found best toprovide the material as rectangular sheets 20 cut to a desirable modulesize suc-h as 4 x 8,

4 x 10,14 x 12 or 4 x 20 feet, as in the manner illustrated at FIG. 1.In field installations the individual sheets may be joined by abuttingtheir adjacent edges 25 together and covering the joints with a strip 26which is bonded to the top surfaces of the sheets as by a mastic 27, asin the manner illustrated at FIG. 3. Another mode of joining the sheetsis to lap the adjacent edges 25 to join the lapped surfaces at the edgesas by mastic 27', as illustrated at FIG. 4, for the sheets, in contrastwith commonly used laminated asphaltic liner sheets, are sufficientlyflexible for such type of joining.

Another mode of handling the membrane-liner is to roll substantiallengths 20 of thematerial as upon a reel 28 having a diameter sufficientas to not unduly bend the membrane-liner. This arrangement, using rolls20' of the material, is especially effective for installa tion of themembrane-liner over comparatively large The liner-membrane 20 may beencased in a structure S as a membrane where there is the possibility ofshrinkage cracks, settlement cracks or fracture for the like occurring,as in the manner illustrated at FIG. 6. The separation of the parts ofthe structures is often sufficient t-o pull .an ordinary membrane apart.As would be anticipated, the felt sheets 23 and the protective outerlayers 24 of asphalt will rupture; however, the central sheet corecomponent 21 is stretched and the core surface layers 22 bonded to itare likewise stretched and necked out to conform w-ith the ductility ofthe central sheet 21. core surface layers 22 will thus protect thecentral sheet from sharp corners which might otherwise cut the sheet.Before the membrane-liner 20 will be completely ruptured the fracturewill ordinarily be widened to such an extent that other ystructuralproblems will also exist which are even more serious than the breakingdown of an effective moisture-holding membrane. When the membraneliner20 is` laid as a mat upon a flat surface B and may -be exposed withoutcover, as in a basin, there is always the danger yof the liner beingpunctured by an o bject being dropped upon it. FIG. 7 illustrates such asituation as where a branch stub of a log L is actually pushed into theliner. This, of course, will tend to push a hole through the protectiveouter layer and through the felt sheets. However, the ductile centralsheet core component 21, protected by the cushioning effect of the feltand the i integrated core layers 22, will be stretched with the latterareas, as in the lining of a basin, since transverse joints areeliminated; however, shipping and handling costs are increased somewhatbecause of the need for increased space and the possible need of a reel28 within each roll. A reel having a diameter in excess of eighteeninches is desirable to properly roll a membrane layer 1a-inch thick.

The central core sheet `21 of a selected synthetic resin may be any oneof several types of polyvinyl chloride and polyvinyl-chloride-acetatematerials now commercially available -as thin ductile, tough sheets, andthe physical properties of the several different types are substantiallythe same insofar as their action in connection with the presentinvention is concerned. It is to be noted that polyvinyl-chloride sheetsare also available as comparatively rigid, hard sheets, but such are notdesired for the purpose at hand, as will be hereinafter explained.

The thickness of the central sheet may vary as desired, according tosheet material, and is commonly available in thickness as from 2 mils-to 30 mils. The preferred thickness is 4 to 10 mils, and it wouldappear that the thicker sheets are unnecessary for most applications.

The ductile types of polyvinyl chloride sheets are expecially suitablefor this purpose because good thermal bonding with compatible asphalt ispossi-ble, as with the manner hereinafter explained, and the syntheticresin is not adversely affected by the constituents of asphalt. Also,the desired types of tough, ductile sheets will stretch to alconsiderable extent before they will rupture or tear. This incombination with a suitable asphalt imparts to the membrane-liner 20 aproperty that does not exist in other types of asphaltic liner sheets,since the proportions of the asphalt forming the core surface layers 22and the physical properties of such asphalt, hereinafter set forth,cooperate with the polyvinyl chloride sheet 21 to supplement itstoughne-ss by incorporating it in a yieldable, plastic medium. This alsovery effectively protects the sheet 21 from deterioration by sunlightand air.

to a substantial degree before rupturing or tearing. It is to be notedthat fragments of the felt will effectively blunt the point of apuncturing object; moreover, the asphalt core surface layers 22 willparallel to a considerable degree the ductility of the sheet 21 and suchwill further tend to cover and blunt sharp edges of the object, such asa branch stub of a log. The felt and core surface layers will therebyact to prevent an actual cutting action through the core component sheet21. Also, it is to be noted that the liner will not ordinarily bepierced by `sharp pointed rocks such as r, illustrated at FIG. 7.

It was discovered that, for a membrane-liner suitable for the uses abovementioned, the type of asphalt appropriate for use in the core surfacelayers 22 was critical. Too soft an asphalt will cause the linermaterial to sag so badly at ordinary temperatures that it cannot behandled. Moreover, in field use, when a membrane-liner is exposed to thesun, it will easily heat up to temperatures as high as and 165 F. and toa point where the component layers of a lsoft asphalt will slip apartfor lack of adequate interbond. At the other extreme, too hard anasphalt core will -be brittle, will crack the protective felt sheets andwill not effectively bond to the ductile polyvinyl chloride sheets.

The best asphalts were found to be unfilled, air-blown asphalts, ortheir equivalents such as might be produced with fillers, having aneffective 20G-235 F. softening point as measured by Ring and Ball TestMethod A.S.T.M. E28 and a 25-42 penetration at 77 F. as measured -byA.S.T.M. Test Method D-5. The preferred material was found to be anair-blown asphalt having a 210-220D F softening point and a 30-40penetration at 77 F. Such asphalts are comparatively stiff but notbrittle at ordinary temperatures. The softest asphalt that can :beconveniently used has a softening point of not less than F. and apenetration of not more than 40 at l 77 F., although a sheet made withsuch asphalt is too l'imber for most pur-poses. It was .also found thatas an upper limit, asphalts having a softening point greater than 245 F.and a penetration of less than 20` at 77 F. were too hard and brittleand would not effectively bond to the polyvinyl chloride sheets.

It was established that the asphalt surface layers 22 of the core shouldbe comparatively thick to effectively hold and protect the central sheet21 and should be much thicker than the adhesive layers ordinarily usedto hold felt `sheets together. It was found that the thickness of Thethe combined core surface layers 22 and central sheet 21 could be fromone-third to two-thirds, and preferably about one-half, the thickness ofthe final laminated material to effectively form a body which willfunctionally protect the central sheet 21. In actual dimensions, athickness of the core comprised of the layers 22 and a central sheet 21may vary from 1/0 to 1/lo-inch and in a finished laminatedmembrane-liner which is 1s-inch thick, a core 1/lG-inch thick ispreferred.

With such thickness, the core surface layers 22 of a selected asphalthaving a 2l0-220 F. softening point and a penetration of -40 at 77 F.are sufficiently ductile to permit plastic deformation and flow ofasphalt under sustained pressure but at the same time provide a sheetsufficiently rigid to be easily handled.

Conventional -asphalt saturated felt sheets or webbin are satisfactoryfor the reinforcing sheets 23. Commercial asphalt saturated felts aremeasured according to their weight and will ordinarily be available aslight as seven pounds per square or as heavy as thirty pounds persquare. The thickness of such felts will Vary from approximatelyone-sixty-fourth inch to one-sixteenth inch and in a finishedmembrane-liner 20 having a nominal thickness of one-eighth inch afifteen pound asphalt saturated felt having a thickness of approximatelyone-thirtysecond inch is preferred.

The asphalt used to saturate these felts is not critical although itshould be somewhat softer than the asphalt forming the core surfacelayers 22 to provide a better take-up and saturation action. A preferredasphalt is a blown asphalt having a 13S-170 F. softening point and a30-50 pentration at 77 F. This type of asphalt will effectively saturatethe felt and at the same time the softening point is at a temperaturehigh enough to avoid trouble in field installations. While the feltlayers impart strength to the final product and adhere to the centralcore surface layers to rigidify the membrane liner, it is to berecognized that the tensile strength and ductility of ordinary felt iscomparatively low and such felts may be otherwise reinforced, ifdesired, by stronger fibrous materials.

The protective outer layers 24 of the membrane-liner are primarily forresisting weathering action and a third type of asphalt may be used forthis purpose. It is desired to have a much harder asphalt and a selectedtype commonly used for weather protection has a 22S-245 F. softeningpoint and a 14-21 penetration at 77 F. This is not a critical limitationhowever. The thickness of this protective layer is likewise not criticaland the layer may be comparatively thin varying from 1/100 to 1/gg-inchand it is contemplated in the manufacture of the membrane-liner 20 thatthis protective layer will be applied and thinly spread onto the outersurfaces of the felt sheets 23.

Several problems exist in the manufacture of a membrane-liner 20constructed according to the invention, with the primary problem beingthat the temperature necessary to melt the core surface layers 22 topermit them to be sufficiently fluid to be properly applied and bo-ndedto the central resin sheet and to the felt sheets is as great as, orgreater than, the softening point temperature of a ductile type ofpolyvinyl chloride suitable for the central core sheet 21. The types ofpolyvinyl chloride sheets having desirable properties of ductility andsoftness will have a comparatively low softening point temperature,which may be as low as 205 F. and which will not exceed approximately300 F. The temperatures required to melt the suitable types of asphalts,having softening point temperatures ranging from 170 F. to 245 F., to apoint where they will be sufficiently fluid to be worked, will vary fromapproximately 320 F. toA 375 F.

It would seem that a polyvinyl chloride sheet having a softening pointtemperature above the asphalt melting temperature would be preferable.Such materials exist and a membrane-liner was made with ahigh-softeningoccur between the resin core sheet 21 and the asphaltc Citsurface layers 22 if they were brought together with the asphalttemperature being greater than the softening point temperature of theresin.

A good, flexible, ductile polyvinyl chloride sheet, having a softeningpoint, that is the point where the material loses its tensile strength,of between 275 F. and 300 F. and which is suitable for the purpose athand, can be furnished by a number of suppliers.

Asphalts which melt below such temperatures, 275 F. to 300 F., to adegree of fluidity which permits them to be easily worked and spread onthe polyvinyl chloride sheets are too soft to be used for the coresurface layers 22. While the suitable materials to provide a proper corelayer could be applied to the central sheet 21 by use of volatilethinners, such a method was not practical.

The preferred asphalt, being a 210220 F. softening point must be heatedto approximately 350 F. to be sufciently fiuid to be easily handled. Toapply this asphalt to a preferred type polyvinyl chloride sheet having asoftening point temperature of approximately 300 F. it can be cooledslightly but not enough to prevent it from softening or melting thesheet. However, it was discovered that there was an apparent time delayin the breakdown and softening action of a polyvinyl chloride sheet inthis range of temperatures which would avail if the manufacture of themembrane-liner could proceed at a sufficiently fast rate. For a veryshort time interval, the polyvinyl chloride sheet would not soften andsever at the point of first contact between the resin and the asphalt.Moreover, subsequent deterioration of the polyvinyl chloride sheet wouldnot be significant if the hot membrane could be promptly cooled off.With such restrictions, the hot asphalt could be applied to thecengr'laslopxlyvinyl chloride sheet at temperatures as high as Thisphenomena is indicated by the graph at FIG. 9. The curve shows therelationship of tensile strength to temperature for a typical polyvinylchloride material. It is to be noted that as the temperature increases,the tensile strength of the polyvinyl chloride will decrease onlygradually until a critical temperature slightly lower than 300 F. isreached. At that point, there is a sudden drop in tensile strength andthe polyvinyl chloride is in a range where the material may be drawn orotherwise Worked and where the material will normally Vshrink as from aplastic memory action. With a slight further increase of temperature,the strength of the material drops to zero, the apparent melting orsoftening point. The discovery herein taken advantage of lies in thefact that the strength-temperature relationship for the polyvinylchloride is different for short initial time intervals than it is aftera heating effect has set in. For a short time interval, for example,less than one second, the polyvinyl chloride will apparently retaintensile strength, and can be worked even at temperatures above theapparent melting or softening point of the material, as shown by thebroken line curve 30. While this phenomena is not fully understood, itis easily demonstrated when manufacturing a membrane-liner according tothe invention, for whenever there is any slowdown of the operation, atthe necessarily high temperatures, as hereinafter described, thepolyvinyl chloride sheet will melt and break where it contacts theasphalt.

The manufacture of the membrane-liner is illustrated in a diagrammaticmanner at FIG. 8. The polyvinyl chloride material for the central sheet21 is furnished as a continuous web in a roll 31. This central sheetmoves from the roll under a small tension and along a substantiallyhorizontal path through the `apparatus as illustrated. The felt sheets23 at the upper side and the under surface of the central sheet 21 arealso provided as continuous webs upon supply rolls 33. These sheets,also under tension, are unwound and move in unison with the movement ofthe central sheet 21. The aphaltic core surface layers 22 are firstapplied to the under side of the upper felt sheet and the upper side ofthe lower felt sheet as from upper and lower applicator rollers 32; Theprotective outer layers 24 of the upper surface and under surface of thesheet are applied subsequently, after the other sheets and layers arebonded together as hereinafter described. The protective layers 24 areconventionally applied as by a roller applicator 34 at the under side ofthe newly-formed sheet 20 and a flow application 34a at the upper sideof the sheet.

In further detail the rolls 31 and 33 are mounted upon suitable shafts35 aud are braked in any conventional manner to apply a desired tensionupon the webs 21 and 23 extending therefrom. The applicator rolls 32 aremounted in suitable reserv-oirs 36 which contain asphalt adapted to becarried upon the roller for transfer to the webs of the layer material22, the asphalt being supplied to the reservoirs 36 by a conventionalmeans.

The webs converge toward and move between a pair of driving-sizing rolls37 which function to compress the felt sheets, core layers and centralsheets together and to hold the thickness of the moving web to aselected value,

lfor example 1A; -inch.

As the combined webs move through the sizing rolls 37, they pass theapplicators 34 and 34a which apply a protective outer layer 24 ofasphalt. sheets move between wiping blades 38 which control thethickness of the protective outer layers 24. Next, the membrane-liner,preferably, moves past a mica applicator 39 which spreads a thin layerof mica on the top surface of the membrane-liner while the asphalt isstill hot and in a tacky condition.

The next step is to move the membrane-liner through a cooling tank 40where it may be submerged in cooling water or cooled by sprays 41 asindicated. As the cooled membrane-liner 20 emerges from Vthe coolingtank, it is then moved past edging rolls 42 which establish the properwidth of the membrane-liner and remove rough edges formed during theoperation. Finally, the finished membrane-liner moves upon a table 43and past a transverse cutter 44 which cuts the membrane liner intofinished lengths as illustrated.

As hereinbefore set forth, the asphalt core cover layers 22 areabnormally thick when compared with the normal applications of asphaltlon-felt sheets and to maintain such thickness, the temperature of theasphalt must be such that it is reasonably viscous. With the preferredZIO-220 F. softening point asphalt, the temperature at the applicatorrolls 32 will be approximately 350 F. to permit a layer 1/,2inch thickto be applied to the felt webbing 23. However, -it is to be recognizedthat the best operating temperature will vary with different batches ofasphalt, but that in continuous operation the operator can quicklyestablish a proper temperature so that the selected thickness of thecore layers 22 will be applied to each felt web 23.

As the central sheet or web 21'moves toward the sizing rolls 37, itpasses underneath a spreading bar 45 which helps eliminate wrinkles thatmay form in the polyvinyl chloride sheet. This bar pushes the centralweb against the'lower felt sheet 23 and against the hot asphalt corelayer 22 on that web. To facilitate guiding and holding the lower feltsheet 23, a support plate 46 may be located underneath it and directlyunderneath the spreader bar 45.

Next, the laminated v Not only does the spreading action of the bar 45tend to smooth lout longitudinally disposed wrinkles which naturallyoccur in the web of polyvinyl chloride, but also the pressing of thepolyvinyl chloride against the hot asphalt holds it in place and causesa slight transverse shrinkage of the synthetic resin. This also assistsinpermitting the synthetic resin sheet to move between the sizing rolls37 lin substantially a wrinkle-free condition.

As hereinbefore set forth, while applying the core surface layers 22,the temperature of the asphalt is greater than the temperature at whichthe polyvinyl cholride sheet will soften or melt. For example, asillustrated at FIG. 10, a curve representative of a core asphalt 22having a softening point temperature of 210-220" F. shows that atemperature range of 320 F. to 350 F. is necessary for the selectedasphal-t material to be reduced in viscosity to a point where it issufficiently fluid to be worked. At lower temperatures, the asphaltincreases in viscosity to the point where adequate bonding and controlof thickness of the application are limpossible. The higher softeningpoint asphalts heretofore mentioned, which can be used for core materialand which .may be bonded to the polyvinyl chloride sheet 21, as theupper limit, must be heated to even higher temperatures with the upperoperable limit being approximately 375 F.

Nevertheless, it was found that'the polyvinyl chloride sheet 21 willretain its strength at high temperatures for short periods of time andit was merely necessary to move the webs through the apparatus atcomparatively high rates of speed. The time interval between the rstcontact of the synthetic resin with hot asphalt, at the spreader 45, andthe movement of the webs past the spreader bar must be in a matter offractions of a second, and the time interval between the rst contact ofthe synthetic resin with hot asphalt at the spreader 45 and the movementof the webs through the sizing rolls 37 must be in a matter of a secondor two at the most.

In operation of the process, it was demonstrated that there is acritical speed and timing for any given thickness of polyvinyl chlorideand any selected temperature of asphalt contacted by the polyvinylchloride. If the process were slowed down, the central web 21 would meltand sever and would have to be rethreaded into the sizing roll. Whenthis condition occurred, the point where the resin softened was at or`adjacent to the spreader bar 45,

close to the first point of contact between the two materi- Y als,suggesting an extremelyv short time period during which the sheetretained strength at the elevated temperatures. After contacting the hotasphalt, the tension on the polyvinyl chloride sheet was released by itsmovement in unison with the asphalt coated lower sheet to which 'it hadjoined. Aside from transverse shrinkage, it was observed that no furtherdistortion or deterioration of the polyvinyl sheet occurred during theshort time interval when the polyvinyl chloride sheet lay upon theasphalt coated lower sheet 23 and before it was enclosed by the upperasphalt coated sheet 23 and bonded between these sheets. Although it wasin a softened condition, it was held in place by the asphalt. Thesubsequent placing of the upper layer of felt and hot 'asphalt did notfurther dis- -turb the polyvinyl sheet, even in its softened condition.

The temperature-material-movement curve 47 at FIG. 1l demonstrates theoperation of the process. At the first point, namely, point a a hot coreasphalt is applied to the lower felt sheet 23. This asphalt coolsslightly in its movement from the point of 'application to the contactpoint b of the spreader bar. The temperature of the polyvinyl chloridesheet 21 at this Contact point is almost instantaneously brought up tothe temperature of the hot asphalt because of its comparative thinness.At the same time, the hot core asphalt 22 is applied to the upper feltsheet as at c and the materials move to their ultimate contact at thesizing rolls, at which time there is a slight increase in temperature asat point d. This effects a bonding and welding together of thecomponents forming the core structure and felt cover and this bondedmaterial moves through and past the sizing rolls to next receive theapplication of the muc-h hotter protective outer layer 24 of asphaltwhich is applied at a temperature indicated at point e. The hotprotective layer at the outside of the membrane-liner graduallyincreases the temperature at the center of the liner to a small degreeas indicated at g. Thence, as the membrane-liner moves through thecooling tank 40, the temperature at the core is rapidly dropped tonormal room temperature as indicated by the curve 47.

This severe treatment of the polyvinyl chloride resin central sheet 21,by embracing it between layers of hot asphalt followed by a suddencooling, effects changes in the characteristics of the material. Asabove noted, some transverse shrinkage of the material was observed.However, the physical deterioration, as by chlorine release which mightbe expected from overheating when the asphalt and the polyvinyl chloridesheets were effectively bonded together did not occur, and it wasapperent that 4the comparatively short time during which the polyvinylchloride was exposed to the elevated temperatures above its softeningpoint was not sufficient to cause deterioration of the polyvinylchloride sheets used.

Distinctive in concept and unique in advantageous practicality, theweld-bonded laminate core comprised from the polyvinyl chloride resinsheet 21 and the asphaltic surface layers 22 in accordance with thetechniques and criteria hereinbefore discussed is significantly novel inrespect of properties qualifying it to function with superior merit asthe essential feature of a membrane-liner. The selection and use ofsuitable ductile asphalt material for the surface layers 22 and theapplication thereof to the resin sheet 21 at briefly-effectivetemperatures higher than that normally disruptive of the resin sheetmaterial, as herein taught, results in an interbonding of theconsequently-softened resin sheet surfaces with the hot fluid of theasphalt layers to establish, when cooled, a welded and integratedcomposite web characterized throughout by strength and ductilityequivalent to the original, such properties evidenced by lthe resinsheet prior to treatment and by a thermal union of its component layersinhibitive of layer separation or relative displacement under any andall non-destructive inuences of intended use.

To study the effect upon short-period elevated temperatures of thepolyvinyl chloride sheets, a membrane-liner was manufactured with, andtests were made wit-h a polyvinyl chloride sheet material manufacturedby the Union Carbide Plastics Company which carried a proprietory labelKDA 2265. It was recommended that this material be used at a maximumtemperature of 175 F. and that it could be worked at an elevatedtemperature of 205 F. for short periods of not more than thirty minutes.However, the application of much higher temperatures did not appear tohave adverse effect on the polyvinyl chloride sheet material.

Since, in the manufacture of the membrane-liner, as above described, thetemperatures far exceeded the recommended maximums, a group ofindicative tests were made at higher temperatures. Strips of thepolyvinyl chloride sheet were heated in an oven to temperatures whichwere as high as 375 F. for various periods of time. The strips \werethen cooled to room temperature and changes in the tensile strength andpercent elongation noted. While these tests cannot be comparable withfolding the polyvinyl chloride sheets between layers of hot asphalt, theindications were that if the polyvinyl chloride sheets were exposed tohigh temperatures for short periods only, no deterioration would occur.

At a temperature of 315 F. exposures up to three minutes did not appearto damage the material, but actually tempered and improved it slightlyby increasing the elongation approximately six percent. Longer exposuresat the temperature of 315 F. showed an effect of deterioration for thenthe tensile strength and elongation were less. When the material wasexposed to a temperature of 375 F., an exposure of 25 seconds increasedthe tensile strength approximately ten percent and the elongationapproximately three percent, while longer exposures severely reducedboth tensile strength and the elongation.

Aging effects upon the polyvinyl chloride were considered, and aspecimen of a membrane-liner were exposed to the weather for more than ayear. The polyvinyl chloride in this material did harden, increased itsstrength and decreased its elasticity but not to a degree which wasconsidered as being serious.

While I have now described my invention in considerable detail, it isobvious that others skilled in the art can devise and build alternateand equivalent constructions which are nevertheless within the spiritand scope of my invention. Hence, I desire that my protection belimited, not by the illustrations and constructions herein described,but only by the proper scope of the appended claims.

I claim:

1. A process for the manufacture of a laminated membrane-liner web,characterized by having a central sheet of a ductile vinyl chloridepolymer having a softening point of 205 F. to 300 F. enveloped betweenand thermally bonded to asphaltic layers of asphalt having a softeningpoint between 170 F. and 245 F. and which is fluid at a temperaturebetweenl 300 F. and 375 F. which asphaltic layers combine with thecentral sheet to form a core and an asphalt saturated reinforcing sheetat each side of the core, including the steps of moving a web of thevinyl chloride polymer between webs of the reinforcing sheets in unisonfrom spread-apart positions along converging paths to interlaminatingcontact, coating the inner surface of each reinforcing sheet with alayer of liquid asphalt of sufficient thickness to form a portion of thecore with the asphalt temperature being, at the time of contact,significantly above the softening point temperature of the vinylchloride polymer, compressing the converging webs as they ycome togetherto a predetermined thickness to form the membrane-liner while moving thewebs together with a rapidity sufficient to envelope the vinyl chloridepolymer before it loses sufficient tensile strength by heat softening tobreak where it contacts the asphalt, and cooling the membrane-linerbefore the heat of the asphalt layers initiates significantdeterioration of the tensile strength of the vinyl chloride polymersheet.

2. In the process defined in claim 1, wherein the softening pointtemperature of the polymer is less than approximately 300 F. and thesoftening point temperature of the asphalt is between 170 F. and 245 F.

3. In the process defined in claim 1, wherein the asphalt temperature,at the time of contact with the polymer, is at least 20 F. above thesoftening point temperature of the polymer.

4. In the process set forth in claim 1, the further steps of applying aprotective coating of asphalt, having a softening point of at least 225F., after the combined sheets alrle sized for thickness and promptlycooling the finished s eet.

5. In the method set forth in claim 1, the further step of pressing thevinyl chloride polymer web against the asphalt coated surface of onereinforcing sheet immediately before the web and the reinforcing sheetconverges with the opposing reinforcing sheet.

6. In the process set forth in claim 5, wherein the time interval ofcontacting the synthetic resin web with one asphalt coated surface andconverging the same to convergence with the opposing coated surface isless than two seconds and the total time interval from first contact ofthe synthetic resin web with the hot asphalt and initiation of coolingthe same is less than five seconds.

' 7. In the process set forth in claim 1, wherein the asphalt formingthe core is heated to a temperature not exceeding approximately 375 F.and the time interval between first contacting the synthetic resin webwith the hot asphalt and cooling the finished liner below F. is lessthan 25 seconds.

8. As an article of manufacture, an asphalt-vinyl chlo ride polymer coresandwiched between asphalt saturated reinforcing sheets at each side ofthe core wherein the core is one-third to two-thirds of the totalthickness of said article of manufacture, said core comprising a centralsheet 2 to 30 mils thick of ductile, stretchable vinyl chlov ridepolymer having a softening point of 205 F. to 300 F. thermally bondedbetween layers of asphalt softening between 170 F. and 245 F. and havinga uid temperature between 320 F. and 375 F., the central sheet of vinylchloride polymer having a softening point temperature significantly lessthan the fluid temperature of the asphalt of the core, each layer ofasphalt of the core being 100 to 200 mils thick, said asphalt beingsufficiently ductile to permit plastic deformation and How thereof undersustained pressure while at the same time providing a core suicientlyrigid to be easily handled.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS6/ 1953 France.

15' EARL M. BERGERT, Primary Examiner.

I. I. BURNS, C. B. COSBY, Assistant Examiners.

8. AS AN ARTICLE OF MANUFACTURE, AN ASPHALT-VINYL CHLORIDE POLYMER CORESANDWHICHED BETWEEN ASPHALT SATURATED REINFORCING SHEETS AT EACH SIDE OFTHE CORE WHEREIN THE CORE IS ONE-THIRD TO TWO-THIRDS OF THE TOTALTHICKNESS OF SAID ARTICLE OF MANUFACTURE, SAID CORE COMPRISING A CENTRALSHEET 2 TO 30 MILS THICK OF DUCTILE, STRETCHABLE VINYL CHLORIDE POLYMERHAVING A SOFTENING POINT OF 205*F. TO 300* F. THERMALLY BONDED BETWEENLAYERS OF ASPHALT SOFTENING BETWEEN 170*F. AND 245*F. AND HAVING A FLUIDTEMPERATURE BETWEEN 320*F. AND 375*F., THE CENTRAL SHEET OF VINYLCHLORIDE POLYMER HAVING A SOFTENING POINT TEMPERATURE SIGNIFICANTLY LESSTHAN THE FLUID TEMPERATURE OF THE ASPHALT OF THE CORE, EACH LAYER OFASPHALT OF THE CORE BEING 100 TO 200 MILS THICK, SAID ASPHALT BEINGSUFFICIENTLY DUCTILE TO PERMIT PLASTIC DEFORMATION AND FLOW THEREOFUNDER SUSTAINED PRESSURE WHILE AT THE SAME TIME PROVIDING A CORESUFFICIENTLY RIGID TO BE EASILY HANDLED.